The invention relates to DC motor rotation speed alarm circuitry, and more particularly, to alarm circuitry that is able to accurately display alarm signals even if the rotation speed of the motor changes.
In modern society, a great amount of electronic data is broadcasted and processed so that information and knowledge are exchanged rapidly. Technological developments accelerate at a faster pace, and people""s lives are greatly enriched. Take notebook computers for instance. When processing a large amount of data, the central processing unit becomes overheated. Hence the notebook computer usually has a control circuit to modulate the operating speed of the radiator to resolve the heat dissipation problem, and alarm circuitry to feed back alarm signals to the computer system to indicate whether the computer system is functioning properly.
Refer to FIGS. 1 and 2 for the heat dissipation procedures of a conventional radiator 10 for a central processing unit (CPU) 12, and a simple circuit diagram of the driving circuit 16 and the alarm circuit 20 shown in FIG. 1. As shown in FIG. 1, the radiator 10 includes a DC motor 14, a driving circuit 16 electrically connected to the DC motor 14, and a radiation fan 18 electrically connected to the DC motor 14. When the radiator 10 performs a heat dissipation procedure to the CPU 12, the driving circuit 16 first transmits a rotation signal to control the rotation of the DC motor 14. The rotation signal is usually a current signal. Then the radiation fan 18 is driven to rotate by the DC motor 14 to perform heat dissipation processes to the CPU 12. Finally, the CPU 12 feeds back signals indicating the result and operating conditions of the heat dissipation procedure, and also whether to modulate the rotation speed of the DC motor 14 to the driving circuit 16. The alarm circuit 20 receives the operating conditions of the CPU 12 transmitted from the driving circuit 16, and outputs an alarm signal to the computer system (not shown in the drawings).
Referring to FIG. 2, the driving circuit 16 includes an n-p-n bipolar junction transistor (BJT) functioning as a switch component 17, which has an emitter connected to the ground GND and a collector electrically connected to the alarm circuit 20. The alarm circuit 20 is connected to a constant voltage power supply Vcc2. In addition, the driving circuit 16 has one node connected to a voltage power supply Vcc1 with a voltage greater than or equal to the voltage of Vcc2.
In order to facilitate description of the operating principle of the alarm circuit 20, the alarm signals described below are represented by digital signals xe2x80x980xe2x80x99 and xe2x80x981xe2x80x99. xe2x80x980xe2x80x99 indicates that the CPU 12 is in a normal operating condition while xe2x80x981xe2x80x99 indicates that the CPU 12 is not operating or is operating abnormally. Another assumption is that the voltage of the first voltage power supply Vcc1 is 12 V (Volts) while the voltage of the second voltage power supply Vcc2 is 6 V.
When the CPU 12 is in a normal operating condition, the DC motor 14 maintains a selected rotation speed, and the current generated by the voltage power supply Vcc1 passes through the switch component 17 and flows to the ground node G through the emitter of the n-p-n BJT 17. In such a condition, there is no electric potential difference between the emitter of the BJT 17 and the ground GND. Hence the voltage received by the alarm circuit 20 is approximately 0 V, and the indication of the alarm signal output by the alarm circuit 20 is xe2x80x980xe2x80x99. This means that the CPU 12 is functioning normally. When the CPU 12 is not functioning, the DC motor 14 does not rotate. The first voltage power supply Vcc1 does not provide power to the switch component 17 (i.e. the BJT 17 does not conduct electrically). The voltage received by the alarm circuit 20 is 6 V (i.e. the voltage provided by the second voltage power supply Vcc2). Then the alarm signal outputted by the alarm circuit 20 indicates xe2x80x981xe2x80x99, meaning that the CPU 12 is not functioning or is functioning improperly.
When data processing volume in the CPU 12 increases, the driving circuit 16 accelerates the rotation speed of the DC motor 14. In such a condition, there is a floating voltage between the driving circuit 16 and the ground GND (i.e. the transistor 17 and the ground GND). The faster the DC motor 14 rotates, the greater the floating voltage becomes. Assuming that the rotation speed of the DC motor 14 increases to a preset level and the floating voltage between the driving circuit 16 and the ground GND is 3 V, the voltage received by the alarm circuit 20 is 3 V. In such a condition, the alarm circuit 20 cannot output the correct alarm signals. When the floating voltage is 6 V (i.e. same as the voltage of the second voltage power supply Vcc2), the alarm signal outputted by the alarm circuit 20 indicates xe2x80x981xe2x80x99. However, the overall computer system is in fact in a normal operating condition, but is processing or transmitting a large amount of data. Therefore, the system could mistakenly judge the situation and cause a system shutdown because of the error signals.
The object of the invention is therefore to provide DC motor rotation speed alarm circuitry that is simply designed with a smaller number of electronic components and can accurately display alarm signals for motor operating conditions even if the rotation speed of the motor has changed, thus enabling the whole system to maintain normal operation.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.